The　flow　boiling　heat　transfer　characteristics　of　subcooled　air-dissolved　FC-72　on　a　smooth　surface　(chip　S)　were　studied　in　microgravity　by　utilizing　the　drop　tower　facility　in　Beijing.　The　heater,　with　dimensions　of　40　×　10　×　0.5　mm3(length　×　width　×　thickness),　was　combined　with　two　silicon　chips　with　the　dimensions　of　20　×　10　×　0.5　mm3.　High-speed　visualization　was　used　to　supplement　observation　in　the　heat　transfer　and　vapor-liquid　two-phase　flow　characteristics.　In　the　low　and　moderate　heat　fluxes　region,　the　flow　boiling　of　chip　S　at　inlet　velocity　V　=　0.5　m/s　shows　almost　the　same　regulations　as　that　in　pool　boiling.　All　the　wall　temperatures　at　different　positions　along　the　heater　in　microgravity　are　slightly　lower　than　that　in　normal　gravity,　which　indicates　slight　heat　transfer　enhancement.　However,　in　the　high　heat　flux　region,　the　pool　boiling　of　chip　S　shows　much　evident　deterioration　of　heat　transfer　compared　with　that　of　flow　boiling　in　microgravity.　Moreover,　the　bubbles　of　flow　boiling　in　microgravity　become　larger　than　that　in　normal　gravity　due　to　the　lack　of　buoyancy　Although　the　difference　of　the　void　fraction　in　x-y　plain　becomes　larger　with　increasing　heat　flux　under　different　gravity　levels,　it　shows　nearly　no　effect　on　heat　transfer　performance　except　for　critical　heat　flux　(CHF).　Once　the　void　fraction　in　y-z　plain　at　the　end　of　the　heater　equals　1,　the　vapor　blanket　will　be　formed　quickly　and　transmit　from　downstream　to　upstream　along　the　heater,　and　CHF　occurs.　Thus,　the　height　of　channel　is　an　important　parameter　to　determine　CHF　in　microgravity　at　a　fixed　velocity.　The　flow　boiling　of　chip　S　at　inlet　velocity　V　=　0.5　m/s　shows　higher　CHF　than　that　of　pool　boiling　because　of　the　inertia　force,　and　the　CHF　under　microgravity　is　about　78–92%　of　that　in　normal　gravity.　©　2018　Springer　Science+Business　Media　B.V.,　part　of　Springer　Nature